The present invention relates to a method of and a burner for burning liquid or gaseous fuels in a firebox with a decreased formation of NO.sub.x, whereby the combustion air is supplied in portions in the form of primary and secondary air, the portions are fed in one after the other at axial intervals parallel to the flow of the combustion gases, and the primary air generates an injector effect that draws combustion gases in.
The combustion air in a burner of this type can be fed in in component currents with the combustion in an initial combustion section being reducing. The combustion air in known pulverized-coal burners is supplied through concentric channels with their exit cross-sections essentially in the same plane (Jahrbuch der Dampferzeugungstechnik, 4th Ed., 1980, 81, pp. 748-763). Decreasing the content of NO.sub.x by recirculating flue gas and mixing it with all or part of the combustion air is also known (DE OS No. 2 306 537 and DE OS No. 3 110 186).
The use of a burner of this type, with air-channel exits in the same plane, as a gas or oil burner resulted in an essentially slighter decrease in NO.sub.x content than that obtained with a pulverized-coal burner. Obviously, the proportions of the gas or oil flame in the burner were not affected as much by the discontinuous supply of air in the same exit place as in a pulverized-coal flame.
An oil burner in which the component currents of combustion air are supplied at intervals along the axis of the burner is known (U.S. Pat. No. 4,004,875). Since the proportion of primary air in that device is lower than that of secondary air, an initial flame can become established with insufficient ultraviolet radiation. Some of the incompletely burned reaction products that occur in the primary combustion section of the burner are also drawn back and returned to that section. These incompletely burned gases lead as the result of cooling and flow-dependent deposition to coke caking and contamination inside the burner. The known burner is accordingly inappropriate for burning heavy heating oil.